The concept, scope and types of flexographic printing inks (1)

First, the concept of flexographic printing ink

     Flexographic printing ink was originally called aniline ink, later called rubber flexographic ink, and is now internationally known as “ flexographic printing ink ” .

     The name of aniline ink is due to the use of aniline dyes in the earliest ink formulations. After 1935 , due to the advances in printing presses and inks, this type of printing method was greatly developed, and its name was finally called “ flexo printing ink ” . China has been its name translated as flexographic ink until 1980 after only according to international collectively be renamed the "flexo ink." Because the plate material used to make this type of plate has changed from the target plate to the target plate , there are photosensitive resins other than rubber.

     Flexographic inks are typical solvent inks, ie, liquid inks, which are dried by evaporation of the solvent. This ink is transferred to the flexographic plate by an anilox roller (dents on the roller). In general, the ink viscosity of 35 mPas · s (25 ° C). This type of ink can be classified into the following three types based on its color body, namely, a dye type, a pigment type, a dye-pigment type. In general, the dye type has a lower viscosity and the pigment type has a higher viscosity to facilitate dispersion and storage (prevention of settling). Due to the different materials of the substrate, the resin and solvent in the ink formulation are also various, but the ink must have suitable viscosity and fluidity, dryness is also required to be good, no residual odor after drying, the printing The adhesiveness of the material is better and it does not work on the printing plate.

     Second, the scope of use of flexographic ink

     Initially, flexo inks were used only for the printing of paper bags , and the range of use was gradually expanded. In the United States, the use of flexographic ink today mostly in packaging printing "target =" _ blank "> field of packaging and printing, about 85%, such as various plastic films, metal foils, cardboard, decorative packaging paper, glass cloth Kraft paper, etc. The use of these packaging printing inks includes those directly printed substrates (ie, surface printing), as well as substrates for making composite structures (ie, printing), and the rest for books, commercials, special printing, etc. In the United States, two-thirds of flexographic inks are water-based flexographic inks, and the rest are solvent-based.At present, flexographic inks are also expanding their application fields and market share in China, because flexographic inks are used in many applications. Basically, good print quality can be achieved on different substrates.

     Third, the application of the type of flexible ink and its configuration method

     From the current state of application, it can be divided into two types from its printed matrix, namely, a porous matrix and a non-porous matrix. Water-based flexographic printing inks are commonly used for printing on the surface of a porous substrate; about two-thirds of the non-porous substrate surface is printed using a solvent-based ink. The use of water-based flexographic inks at home and abroad is an increasing trend.

1 . Type: As described above, the flexographic ink is liquid ink, and its drying method is to penetrate into the substrate (paper) or to volatilize the solvent.

2 . Formulation: The solvent used in this low viscosity ( 100-250 cps) liquid ink is based on the polymer in the dissolving ink. Typical solvents used are water and alcohol, as well as small amounts of glycol ethers, oximes, and aliphatic hydrocarbons. Its film-forming polymers are polyamides, nitrocellulose, rosin, shellac, and acrylates, which are usually used to modify one of these polymers (eg, nitrocellulose can increase heat resistance. Polyamide can increase gloss and flexibility). In most flexographic inks, two or more polymers or solvents are generally used to achieve a balance in performance. The flexographic ink system typically contains 7 to 15 different components. These components make up the general category of pigments, polymers, solvents, and additives used in typical flexographic inks.

     The following is a brief description of the preparation of solvent-based inks and water-based flexographic inks:

1 . Solvent-based flexographic inks: As mentioned above, solvent-based flexographic inks are formulated primarily for printing non-porous substrate surfaces.

     About 75 % of the plastic inks use alcohol-soluble polyamidoamine resin, which represents the reference formula as follows:

     Note: * If a white ink based on TIO2 : is manufactured, this amount can be doubled to reduce the amount of ethanol.